CN1666142A - Reflective stereoscopic display - Google Patents

Abstract

An apparatus comprising a first cell ( 10 b), said first cell comprising a plurality of first elements ( 34 b), said first elements being controllable between a non-reflective state, in which electromagnetic radiation having a first polarization is reflected to a first extent, and a reflective state, in which said electromagnetic radiation having a first polarization is reflected to a second extent, said second extent being greater than said first extent. Said apparatus further comprises a second cell ( 10 a), superimposed on the first cell, said second cell comprising a plurality of second elements ( 34 a), said second elements being controllable between a non-reflective state, in which electromagnetic radiation having a second polarization is reflected to a third extent, and a reflective state, in which said electromagnetic radiation having a second polarization is reflected to a fourth extent, said fourth extent being greater than said third extent. Said first and second elements are arranged so that said first polarization is different from said second polarization.The apparatus can be used in a reflective stereoscopic display.

Description

Reflective Stereoscopic Display

The invention relates to a device comprising a first unit comprising a plurality of first elements which can be controlled between a non-reflective state and a reflective state, in the non-reflective state having Electromagnetic radiation of a first polarization is reflected to a first degree, said electromagnetic radiation having the first polarization is reflected to a second degree in the reflective state, said second degree being greater than said first degree; and placed in the first a second unit on the unit, the second unit comprising a plurality of second elements controllable between a non-reflective state and a reflective state in which electromagnetic radiation having a second polarization is reflected To a third degree, said electromagnetic radiation having the second polarization in the reflective state is reflected to a fourth degree, said fourth degree being greater than said third degree.

The invention also relates to a reflective display comprising a device of the type described above, and to a portable device comprising such a reflective display.

The invention also relates to a method of providing varying brightness in a device of the type described above.

The invention finally relates to a method of providing two images in a reflective display comprising a device of the type described above.

Biological evolution on our planet has provided a variety of organisms with two eyes that are spatially separated from each other within the head and thus have separate but not necessarily distinct visions. Natural selection has clearly demonstrated that it is advantageous if these two separate fields of view are arranged to substantially overlap each other, thereby providing the brain with two slightly different perspectives of the observed environment, which is able to combine the provided information and use it to estimate the distance to the observed object. Determining distance and the difference in distance using both eyes is commonly referred to as stereopsis.

The prior art includes several so-called stereoscopic displays, which thus aim to provide users with a more realistic perception of different kinds of displayed images, such as 3D movies (more formally called anaglyphs). Stereoscopic vision enhances the degree of reality the user experiences compared to standard non-stereoscopic display devices and has its advantages in various applications in entertainment (eg movies, games, etc.) and education (eg flight simulators). Stereo vision will also be advantageous in various other applications, for example in so-called telemedicine, where the stereoscopic perception of a research object such as a human organ by a remote medical expert will excellently aid in various diagnostic and therapeutic applications.

A basic method of providing a user with the perception of stereopsis (i.e., the perception of depth in an image) involves providing two different images, one for each of the two eyes of the viewer, corresponding to Two perspective views, preferably corresponding to the perspective views that an observer would normally acquire if he or she studied the object being described from a certain distance using both eyes.

Usually displays are designed and arranged in such a way that both eyes of the viewer are able to see two images, which is why current methods of providing a stereoscopic experience require providing the viewer with glasses which include a selection in some way for each The image of each eye, thereby presenting the appropriate perspective to the device of each eye. Another way to describe the current approach is to state that a single display device presents two separate programmed perspectives, and provide the user with glasses that decode the individual perspectives so that each eye receives only one specified perspective.

The prior art consists of a device based on a perspective encoding two colors, eg red and green respectively, and providing glasses containing red and green filters. A disadvantage of prior art solutions is that they do not provide a stereoscopic experience in colour.

The prior art also includes glasses that alternately provide two perspective views and that include alternating shutters; a method that requires the viewer to use cumbersome and expensive equipment with a fragile structure that will eventually shatter; or that The expensive equipment has an unbearable weight, which makes long-term use of this equipment impossible, and moreover requires computer power and fine-tuning clocks especially when the two shutters of the two observers simultaneously observe the same two sequentially projected images.

Finally, the prior art also consists in alternately providing two perspectives encoded using polarization, ie the light of the two perspectives has a different polarization, and providing decoding glasses comprising polarizing means.

A disadvantage of all prior art stereoscopic devices is that they are only transmissive (this is sometimes an inherent consequence of the polarization process), where the overall transmitted intensity is generally reduced.

Stereoscopic display devices have been disclosed in European Patent Application EP0349692 "Stereoscopic display", incorporated herein by reference. Said application describes a stereoscopic display capable of displaying a monochrome or color view of a moving, three-dimensional scene, the display comprising means for sequentially alternately projecting the right Each of successive pairs of essentially monochrome images of eye and left eye perspectives. Variable polarizers are used to cycle polarize alternate images in respective opposite scenes in synchronization with their projection rates. These images are analyzed by highly transmissive glasses comprising at least one pair of oppositely sensed cholesteric structured liquid crystal polarizers tuned to the specific color wavelengths of the images and placed on each A cholesteric structure liquid crystal polarizer to transmit only properly polarized images to the corresponding glasses.

The device has several disadvantages which make it unsuitable for several important applications where stereoscopic vision is an advantage. Like other prior art stereoscopic devices, the device is a transmissive display and thus requires a backlight unit.

Furthermore, the device includes means for providing sequential projections of images, which are often noisy and subject to mechanical strain during operation. Ultimately, these features lead to increased power consumption, mass, and volume, which means that implementing such a stereoscopic display in a portable device will bring many disadvantages.

Furthermore, the pictures from the device are projected sequentially, which is accompanied by an unfortunate loss of quality, since normal vision implies a continuous provision of images, ie images of the observed environment are received simultaneously by both eyes.

Another problem is that images are projected sequentially even when not required, as in the case of projecting the same image, such as a typical 2D image, which is also a disadvantage because unnecessary power consumption and a large amount of technology are used.

A big disadvantage of prior art devices is therefore that they cannot provide 2D and 3D images respectively alternately or even simultaneously.

Furthermore, the underlying technique deprives the user of the possibility to modulate the brightness, since he or she is already wearing the requisite glasses, a reduction in brightness that cannot be obtained through traditional methods, such as the use of sunglasses.

Furthermore, the device is not suitable for three separate images with three designated recipients, but is limited to providing the same stereoscopic experience no matter how many observers there are.

In the prior art, liquid crystal displays have been proven suitable for various applications requiring compactness and low power consumption. A liquid crystal display (LCD) is a flat panel display that has the advantages of small size, thin thickness, and low power consumption.

Liquid crystal displays have been used in association with portable devices such as mobile phones, portable computers, electronic calendars, electronic books, television or video game controls, and various other office automation equipment and audio/video machines.

LCDs control the electric field applied to liquid crystal material with dielectric anisotropy to transmit or cut off light, thus displaying pictures or images, all of which are themselves recognized by those skilled in the art and will be briefly explained. Unlike displays that generate light internally—such as electroluminescence (EL) devices, cathode ray tubes (CRTs), and light emitting diodes (LEDs)—LCDs use external light sources.

LCD devices are roughly classified into transmissive type devices and reflective type devices according to methods of using light. In addition to a liquid crystal panel having a liquid crystal mixture injected between two transparent substrates, a transmissive LCD includes a backlight unit for supplying light to the liquid crystal panel. However, it is difficult to manufacture a thin and lightweight transmissive LCD. In addition, the backlight unit of the transmissive LCD has excessive power consumption.

In contrast, reflective LCDs include a reflective liquid crystal display panel, and transmit and reflect natural and ambient light to and from a display screen without a backlight unit.

Since all reflective LCDs must display transmissively, especially because of the inherent reduction in light intensity during polarization, reflective LCDs are not suitable for any prior art stereoscopic devices.

A basic liquid crystal display can be easily constructed by coating two separate sheets of a transparent material such as glass or plastic with a transparent metal oxide. Preferably, the metal oxide is coated in the shape of parallel lines on each separate plate and constitutes the row and column conductors of the LCD. When the two plates are superimposed with the row conductors perpendicular to the column conductors, the rows and columns form a matrix of pixel elements. The row conductors further serve to set the voltage across the cell, which is necessary for directional translation.

An alignment layer (also sometimes referred to as an alignment layer) is applied to each board. The alignment layer may have been rubbed to form a series of fine grooves that are parallel and help the contained liquid crystal molecules to align in a preferred direction, the longitudinal axes of the liquid crystal molecules are parallel to these grooves, and these grooves are along the alignment layer" anchors" these molecules and helps align the molecular twists between the layers.

One of these sheets was coated with polymer spacer beads. These beads maintain a uniform gap between the glass plates where the liquid crystals will eventually be placed. The two glass panels are then brought together and the edges are sealed with epoxy. Leave one corner unsealed for injection of liquid crystal material under vacuum. Once the display is filled with liquid crystals, the corners are sealed and a polarizer (transparent layer with lines) is applied to the exposed glass surface.

The display is completed by connecting the row and column conductors to driver circuits, which control the voltages applied to the various regions of the display.

It is an object of the present invention to provide a display suitable for alternately displaying 2D and 3D images.

In general, the essence of the invention is that if a display is made using two liquid crystal cells in a new and special way, the display will have superior performance and several new features. Best of all, the display can be used both as a stereoscopic display and as a standard 2D display. In addition, this new display design offers many other features, such as enhanced brightness control, the possibility of providing several images to several recipients, and since the construction consists essentially of two units, one can be damaged when the other or act as a backup unit in case of failure. Several embodiments are described, including those that do not require the user to use glasses to experience stereoscopic. For illustration purposes, only one wavelength of light is discussed, but a full-color stereoscopic display in a portable device could be a commercial product incorporating the present invention.

According to a first aspect, the invention relates to a device comprising a first unit comprising a plurality of first elements, said first elements being controllable between a non-reflective state and a reflective state, in electromagnetic radiation having a first polarization is reflected to a first degree in the non-reflecting state, said electromagnetic radiation having the first polarization is reflected to a second degree in the reflecting state, said second degree being greater than said first degree; and a second unit placed on the first unit, said second unit comprising a plurality of second elements controllable between a non-reflective state and a reflective state, having a second polarization in the non-reflective state The electromagnetic radiation of is reflected to a third degree, and in the reflective state said electromagnetic radiation having the second polarization is reflected to a fourth degree, said fourth degree being greater than said third degree, wherein said first and second The elements are arranged such that said first polarization is different from said second polarization.

Preferably, the electromagnetic radiation has a wavelength of 300nm-800nm (ie visible light), and said first polarization and said second polarization are circular polarizations with opposite hand shapes.

This configuration can optionally be achieved by arranging a polarization-changing element (preferably a suitable half-wave plate) between said first and second units, in which case the first and second units are arranged to reflect the same hand-shaped of circularly polarized light. The polarization changing element may comprise a lens. The first and second units may be selected to be at a distance from the optical element or from each other.

The first and second units are preferably arranged to transmit the first and second images to the first and second eyes of a viewer. The wavelengths of the light respectively reflected by the two units do not have to be the same. Preferably said first and second cells are at least partly made of cholesteric structured liquid crystals (CTLC).

According to a second aspect, the invention relates to a reflective display comprising a device of the aforementioned type.

According to a third aspect, the invention relates to a portable device comprising said reflective display. The portable display is preferably, but not necessarily, one of a mobile phone, laptop computer, electronic calendar, electronic book, television or video game control.

According to a fourth aspect, the invention relates to a method of providing brightness variation in a device of the aforementioned type. This method of providing different brightness levels can also be applied to devices comprising more than two units.

According to a fifth aspect, the invention relates to a method of providing two or more images in a reflective display comprising a device of the aforementioned type. Preferably, the method can be used to provide different images for the left eye and the right eye respectively, and the images are preferably perspective views of observed objects or environments respectively corresponding to the left eye and the right eye. The method can be used to provide the possibility to switch between 2D and 3D vision using the same device.

These and other aspects, features and advantages of the invention will become apparent by elucidation with reference to the following examples.

Fig. 1 is a schematic side view of a part of a first preferred embodiment of a liquid crystal display according to the present invention.

Fig. 2 is a schematic side view of a second preferred embodiment of a liquid crystal display according to the present invention.

Fig. 3 is a schematic side view of a third preferred embodiment of a liquid crystal display according to the present invention.

Figure 4 is a typical prior art arrangement for controlling and driving an electro-optical display device.

Figure 5 is a graph showing the relationship between the reflection and the field strength on the applied liquid crystal mixture for a predetermined wavelength.

Figure 6 is a graph showing the percent reflectance as a function of wavelength in order to illustrate the wavelength dependence of the reflective properties of three different liquid crystal mixtures.

Fig. 7 shows a situation where a viewer experiences simulated stereopsis.

Fig. 8 shows another situation where the observer experiences simulated stereopsis.

Fig. 9 shows another situation in which three observers receive three different images from the same screen.

Embodiments of the present invention will now be described with reference to Figures 1-9 of the drawings. The same elements are denoted by the same reference numerals in the various figures.

Fig. 1 is a schematic side view of a part of a preferred embodiment of a liquid crystal display according to the present invention. For illustration purposes, various dimensions, such as the molecular size and the distance between glass plates, are exaggerated, and the molecular structure of the liquid crystal mixture is simplified.

Two cells 10a and 10b each comprising their own matrix of elements or pixels are arranged on top of each other. A thin glass plate 30a, 31a, 30b, 31b partially surrounds each of the two units shown from opposite sides which form substantially parallel planes. In order to reduce the parallax between layers, a plastic substrate can be used instead of glass, because the plastic substrate can be made thinner than glass.

Each cell 10a, 10b comprises its own set of column conductors 12a, 12b and row conductors 14a, 14b arranged on said glass plate 30a, 31a, 30b, 31b according to a prior art LCD, said column conductors and row conductors being The conductors are realized by indium tin oxide (ITO) wires.

In order to orient the surrounded liquid crystals 34a, 34b in a preferred manner, as shown, within each cell are arranged alignment layers (also called alignment layers) 32a, 33a, 32b, 33b, wherein each alignment layer may be Alignment layer SE7511L from Nissan Chemical Industries.

According to the prior art liquid crystal display, it is preferable to use spacer balls (not shown) such as Sekisui Chemical's SP-2050, and a sealing material such as Mitsui Chemical's XN21-S to surround the upper unit 10a on the thin glass plates 30a and 31a. (CTLC cell 1)) and the thin glass plates 30b and 31b (surrounding the lower cell 10b (CTLC cell 2)) are established at a uniform interval.

Appropriate liquid crystal mixtures (CTLC materials) 34a, 34b are arranged in the upper and lower cells, respectively. In this case, 34a is the liquid crystal mixture BL87/BL88 10:90 w:w (Merck) for the upper unit 10a, and 34b is the liquid crystal mixture BL87/BL95 3:97 w:w (Merck) for the lower unit 10b ), so that the two cells contain a mixture of liquid crystals with opposite twists, ie they reflect circularly polarized light with opposite hand shapes.

Those skilled in the art will understand that CTLC materials are a mixture of different types. Basically two types are required: nematic host and chiraldope. The hand shape of the optical active agent determines the hand shape of the CTLC, and the concentration of the optical active agent determines the wavelength (color) of reflected light. To make a color display, there are two basic possibilities: make pixels that reflect different colors, or stack cells that reflect different colors on top of each other.

It is also possible to change the color of the CTLC-hybrid by applying a high electric field perpendicular to the helical axis using an electrode arrangement, which is a conceivable way to achieve a full-color, 3D display using only two layers.

It will be appreciated that in some applications an isolation layer is required between two cells to prevent crosstalk between the row and/or column conductors of the two cells, particularly crosstalk between row conductor 14a and column conductor 12b. It is also conceivable that the lower substrate 31a of the upper cell 10a and the upper substrate 30b of the lower cell 10b may be implemented by a single substrate, possibly including shared column and/or row conductors.

2 is a schematic side view of an alternative embodiment of a liquid crystal display according to the invention, wherein two cells 10a, 10b comprising CTLC-mixtures 34a, 34b are stacked on top of each other, and wherein An optical element 35 is introduced between each unit. For the sake of simplicity, the optical elements are shown at a distance from the upper and lower units 10a, 10b.

Optical element 35 may be a polarization changing element such as a half-wave plate or another suitable optical component that allows circularly polarized light to be redirected from a left-handed to a right-handed orientation, or vice versa.

This structure allows both cells 10a, 10b to be filled with the same liquid crystal mixture, which may be the aforementioned liquid crystal mixture BL87/BL88 10:90 w:w (Merck) or other suitable liquid crystal mixtures.

In the preferred embodiment described above with reference to Figure 1, if both cells comprise the same liquid crystal mixture, the light reflected by each cell will have the same polarization. However, in the embodiment of FIG. 2 , light reflected from one of the cells will pass through the optical element and thus change its polarization, using light of two different polarizations so that two images are transmitted, one from each cell 10a, 10b image.

Alternatively, the optical element may be a lenticular plate as described in US-6,064,424 or US-6,118,584, which are incorporated herein by reference.

According to an aspect of the invention, the above-described embodiment will have the advantage that light reflected from the two units 10a and 10b will be reflected in slightly different directions. If the device is in a small portable device such as a personal digital assistant (PDA) or cellular phone, these directions are preferably arranged to coincide with the left and right eyes of a viewer 0-50 cm from the display, respectively. This embodiment enables the observer to experience stereopsis without eyes.

According to another aspect of the present invention, the embodiment shown in FIG. 2 can be realized as a large-size display, such as a two-person TV. The angles at which the two units reflect light may be arranged to coincide with the positions of the first and second observers seated some distance apart.

It is also conceivable that only some of the displays in a display have the embodiment described with reference to FIG. 2 . For example, the bottommost part of the screen can be constructed according to the invention to allow two viewers to watch a television program and see two different subtitles in two different languages, or to store exchange data or short news reports (as they appear on many televisions). channel), where the lowest space on the TV screen is allocated for storing exchanged data, latest news reports, etc.

In addition to the lenticular plate, the optical element may comprise further optical elements, such as half-wave plates as previously discussed with reference to FIG. 2 .

Fig. 3 is a schematic side view of another alternative embodiment of a liquid crystal display according to the invention, wherein, in addition to the illustration of Fig. Different angles to reflect light. The fact that the CTLC-hybrids 34a, 34b confined in the cell reflect opposite-handed polarized light (or are arranged to reflect opposite-handed polarized light by the optical element 35 as described above with reference to FIG. 2 ), and the The fact that the cells are substantially transparent to light reflected by other cells means that the light emitted from the first and second cells 10a, 10b does not interfere with other light.

Figure 4 shows a schematic diagram of a typical prior art arrangement for controlling and driving an electro-optic display device. In this configuration, liquid crystal display 10 has a matrix of pixels arranged vertically in columns and horizontally in rows. These pixels are located at the intersections of column conductors 12 and row conductors 14 . Column conductors 12 provide an analog voltage to the pixels in each column, while row conductors 14 provide a switching voltage for each associated row, allowing the column voltage to be supplied to the pixels in that row.

The rows are addressed consecutively in a predetermined order by the row decoder 16, which drives each of the plurality of row drivers 18 consecutively.

The column voltages are provided by column driver circuits (implemented as track-and-hold circuits). These track-and-hold circuits receive the ramp voltage from the output buffer amplifier of the digital-to-analog converter (DAC) 22 . DAC 22 receives a continuous digital signal from counter 24, which counts pulses generated by clock 25. The count starts from some minimum or maximum number and steadily increases or decreases until it reaches the opposite end of the scale - the maximum or minimum number, respectively. The DAC thus produces a ramp signal that approximates an increase or decrease of its digital input in a repeating cycle.

The output of the counter 24 is also provided to a plurality of comparators 26, one for each column. This number is then compared in each comparator to a digital number representing the ideal brightness level of the pixel in the associated column. A number representing this brightness level is stored in the associated pixel register 28 during each complete cycle of the system.

When the count provided by counter 24 is equal to the number of digits stored in the pixel register, each comparator 26 generates a pulse that is sent to the track-and-hold circuit for that column. Upon receipt of such an enable pulse, the associated column driver stores a voltage equal to the immediate output of the ramp generator.

Once each ramp period is complete, the voltage stored in the column driver circuit is supplied to the pixels in the particular row selected by the row driver 18 .

Each unit in the device according to the invention can thus be controlled by this prior art arrangement for controlling and driving the electro-optical display device.

Fig. 5 is a graph showing the relationship between reflection and the strength of the electric field applied across the liquid crystal mixture for predetermined wavelengths. Depending on the strength of the applied field, the molecules in an LCD pixel can switch between light and dark, or sometimes (gray scales). How the molecules respond to voltage is an important property of this type of display. The electrostrictive response determines the reflection of light through the cell.

Figure 6 is a graph to illustrate the wavelength dependence of the reflection properties of three different liquid crystal mixtures (i.e.: 90%/10% BL088/BL087, 80%/20% BL088/BL087, 97%/3% BL095/BL087) , showing percent reflectance as a function of wavelength.

It will be understood by those skilled in the art that the dependence of reflected light on wavelength for different mixtures (proven) can be used to fabricate displays, or by filling pixels with three different mixtures to construct full-scale displays such as RGB-displays. For a color display, each of the three different mixtures reflects substantially red, green, and blue light, respectively.

Fig. 7 shows a situation where a viewer experiences simulated stereopsis. The display 40 according to the invention is arranged at a distance 41 from an observer (not shown). Display 40 includes two superimposed liquid crystal cells 10a and 10b as previously described with reference to FIGS. 1-3. Each of these units is connected to the necessary electronics. As shown in FIG. 7, the upper unit 10a presents an image 42a, and the lower unit presents an image 42b. To the naked eye, both images will appear on the display. However, the images 42a, 42b use polarization encoding because the two cells 10a, 10b are arranged to reflect circularly polarized light of opposite hand shape.

The viewer wears an eye-mounted item 43 (depicted as an ocular for purposes of illustration). The observer's left and right eyes observe the screen through polarizing devices 44a and 44b, respectively, which serve as filter elements, and each polarizing device is highly transmissive to one hand type of circularly polarized light. Circularly polarized light of the opposite hand type is not transmitted. Thus, only image 42a produced by upper unit 10a is seen by the observer's left eye through filter element 44a, and only image 42b produced by lower unit 10b is seen by the observer's right eye through filter element 44b.

When the image 42a transmitted by the upper unit 10a is a perspective corresponding to the perspective of the left eye, and the image 42a transmitted by the lower unit 10b is a perspective corresponding to the perspective of the right eye, the result is thus a perspective for the left and right eye respectively. Two separate perspective views, so users experience stereoscopic vision.

Clearly, these two separate perspectives can be the same image experienced by the user regardless of whether he or she wears the necessary eyewear in the stereoscopic feature.

The above-mentioned stereoscopic features of the invention require an eye-wearing article comprising an optical filter element, which may be realized eg as spectacles, the lenses of which comprise suitable polarizing means. These can be made in several ways, for example by absorbing polarizing films for LCDs combined with 1 ambda/2 retardation films used for LCDs. The orientation of the ordinary and extraordinary axes relative to the absorption axis of the polarizing film determines which hand types are absorbed and which are transmitted. Parts can be purchased from Nitto-Denko or Sumitomo Chemical. CTLC films can be made to reflect light of one circular polarization and transmit light of the other. However, these membranes are relatively expensive.

In a preferred embodiment, the on-eye article can be realized as spectacles, but it is also possible to realize the on-eye article as a contact lens.

Fig. 8 shows an embodiment already (partially) illustrated in Figs. 2 and 3 and described with reference to the preceding figures, which does not require the user to use decoded items worn on glasses to experience stereopsis. This is because the units 10a, 10b of the device are arranged so that the images formed by the two units travel in slightly different directions as shown, so that they coincide with the left and right eyes of the user at a certain distance .

The figure shows a deviating optical element, such as a lens sheet 35, arranged between the units 10a, 10b to deflect light reflected from the lower unit 10b into a direction slightly different from that of light reflected from the upper unit 10a. . However, a similar effect can also be obtained using the embodiment described with reference to Figure 3, since this means viewing the two units from slightly different distances and thus from different angles. It is also conceivable to establish a deviation of the direction of propagation of one of the cells by simply tilting one of the cells in contrast to the previous embodiment in which the cells are superimposed on each other, their glass sheets 30a, 31a, 30b, 31b being substantially parallel to each other.

Although the preferred embodiment may be used in portable equipment, other situations are also conceivable in which the arrangement according to the invention proves useful.

Fig. 9 shows a user situation in which an apparatus according to the invention is used to provide different images for multiple users.

A large liquid crystal display 50 is arranged on a wall, for example, in the passenger compartment of an aircraft, within the field of view of three passengers 52a, 52b, 52c who are in different parts of the aircraft and facing the liquid crystal display. The display includes three different layers (not shown), each reflecting light with specific wavelength and polarization properties. For illustration purposes, each of the three units projects one of the images 51a, 51b, 51c.

Three decoding elements 53a, 53b, 53c are arranged in front of each observer, said decoding elements being arranged to substantially transmit only light from one of the cells to each observer. Thus, as shown, observer 52a perceives only image 54a, observer 52b perceives only image 54b and observer 52c perceives only image 54c.

For the sake of simplicity, the decoding elements are shown as screens, but it is also possible to realize them as eye-wearing items (such as glasses) already described above.

A display according to the invention may additionally comprise a backlight unit, or it may be implemented as a portable or large-scale transmissive display.

When the device according to the invention is used as a normal display, ie a 2D display (without glasses), each eye will receive light reflected from the two layers of the device. This means that, as a display device, the device according to the invention has several advantages over the prior art. Only one unit can be used at a time, and the second unit can be used as a backup if the first unit fails.

Since brightness is an important feature in liquid crystal displays, it is advantageous to use a display device according to the invention as a display device that can provide the user with the option to select a brightness level. This can be achieved in practice by instructing only pixels in one layer to reflect light when lower brightness is required, and instructing pixels in both layers to reflect light when high brightness is required. Since the layers reflect circularly polarized light with opposite hand shapes, there is no interference between the reflected light, resulting in a sharp image.

This method of providing different brightness levels can be extended to devices comprising more than two superimposed units. When low brightness is required, N units (N is at least 1, but not equal to the total number of stacked units) can be made to reflect light, and when higher brightness is needed, N+1 stacked units can be made to reflect light.

The apparatus according to the invention may also be, for example, a separate, stand-alone unit, or may optionally be incorporated in a mobile terminal for telecommunications networks such as GSM, UMTS, GPS, GPRS or DAMPS, or other existing types of portable equipment such as Personal Digital Assistants (PDAs), Palmtops, Laptops, Electronic Hitachi, Electronic Books, Television or Video Game Controls), and various other office automation equipment and audio/video machines, etc. or in combination with them.

The invention has mainly been described with reference to a few embodiments. However, other embodiments than the ones described above are equally possible within the scope of the invention as defined by the appended claims. Terms used in the claims should be interpreted according to their ordinary meanings in the technical field, unless explicitly defined otherwise. All references to "a/the [element, device, component, member, unit, step, etc.]" should be construed broadly to mean at least one instance of said element, device, component, member, unit, step, etc. The steps of the methods described herein do not have to be performed in the exact order disclosed, unless explicitly stated.

Claims (24)

1. A device comprising: A first unit comprising a plurality of first elements controllable between a non-reflective state and a reflective state in which electromagnetic radiation having a first polarization is reflected to the first degree, the electromagnetic radiation having the first polarization is reflected to a second degree in the reflective state, the second degree being greater than the first degree; and a second unit superimposed on the first unit, the second unit comprising a plurality of second elements controllable between a non-reflective state and a reflective state having a second polarization in the non-reflective state the electromagnetic radiation is reflected to a third degree, in the reflective state said electromagnetic radiation having the second polarization is reflected to a fourth degree, said fourth degree being greater than said third degree, It is characterized in that said first and second elements are arranged such that said first polarization is different from said second polarization. 2. A device according to claim 1, wherein the electromagnetic radiation has a wavelength of 300 nm to 800 nm. 3. Apparatus according to claim 1 or 2, wherein said first polarization and said second polarization are hand-opposite circular polarizations. 4. The apparatus according to claim 1, wherein a polarization changing element is arranged between said first and second units. 5. The apparatus of claim 4, wherein said polarization changing element is a half wave plate. 6. The apparatus according to claim 1, wherein at least one lens is arranged between said first and second units. 7. The apparatus according to claim 1, wherein said first and second units are spaced apart from each other by a distance. 8. Apparatus according to claims 6 and 7, wherein said first and second units are arranged to transmit the first and second images to the first and second eyes of a viewer. 9. The apparatus of claim 1, wherein said first and second electromagnetic radiation have different wavelengths. 10. The device of claim 1, wherein at least one of said first and second cells is at least partially made of cholesteric structured liquid crystal (CTLC). 11. A reflective display comprising a device according to claim 1. 12. A portable device comprising a reflective display according to claim 11. 13. A portable device according to claim 12, wherein said device is one of the following: a mobile phone, a portable computer, an electronic calendar, an electronic book, a television or a video game control. 14. A method of providing brightness variation in an apparatus as defined in claim 1, the method comprising the steps of: operating elements in one of said first and second cells to their reflective state when lower brightness is required, and When higher brightness is required, the stacked elements in the first and second cells are substantially manipulated into their reflective state. 15. A method of providing brightness variation in an apparatus as defined in claim 1, said apparatus further comprising at least a third unit comprising a third element, said element being controllable between non-reflective and reflective states, Third electromagnetic radiation having a third polarization is reflected to a fifth degree in the non-reflective state, said third electromagnetic radiation is reflected to a sixth degree in the reflective state, said sixth degree being greater than said fifth degree, so Said method comprises steps: When lower brightness is required, basically manipulating stacked elements in N cells to their reflective state, N equal to or greater than 1 but less than the total number of cells, and When higher brightness is required, the stacked elements in the N+1 cells are basically manipulated to their reflective state. 16. A method of providing two images in a reflective display according to claim 11, the method comprising the steps of: operating the first element to reflect electromagnetic radiation in the shape of a first image comprising electromagnetic radiation having a first polarization, The second element is operated to reflect electromagnetic radiation in the shape of a second image comprising electromagnetic radiation having a second polarization. 17. A method according to claim 16, wherein said means in said reflective display further comprises at least one third unit comprising a third element operable to control said An element in which third electromagnetic radiation having a third polarization is reflected to a fifth degree in the non-reflecting state, said third electromagnetic radiation is reflected to a sixth degree in the reflective state, said sixth degree being greater than said fifth degree To an extent, the method includes the steps of: The third element is operated to reflect electromagnetic radiation in the shape of a third image comprising electromagnetic radiation having a third polarization. 18. A method according to claim 16 or 17, wherein said method comprises the steps of: providing at least two separate filter elements, a first of which is capable of transmitting electromagnetic radiation having said first polarization and not transmitting electromagnetic radiation having said second polarization, and the The second of said two filter elements is capable of transmitting electromagnetic radiation having said second polarization but not transmitting electromagnetic radiation having said first polarization, arranging a first filter element between the reflective display and any intended recipient of the first image produced by the first element, and A second filter element is arranged between the reflective display and any intended recipient of the second image produced by the second element. 19. A method according to claim 16, wherein said method comprises the steps of: The first and second elements are arranged to transmit the first and second images in different directions. 20. A method according to claim 19, wherein said first and second units are arranged to transmit the first and second images to first and second eyes of a viewer. 21. The method of claim 18, wherein the first and second filter elements are arranged respectively in front of the left and right eyes of the viewer. 22. A method according to claim 19 for use with an apparatus according to claim 8, wherein the first image and the second image are adjusted to coincide with left and right eyes of a viewer. 23. A method according to any one of claims 16 to 22, wherein the first and second images are identical. 24. A method as claimed in any one of claims 20 to 22, wherein said first and second images are perspective views which create a 3D perception when viewed.

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